Contemporary robotic work tools are becoming more and more advanced and are able to perform more and more advanced tasks such as executing advanced operation patterns. In the example of lawnmower robots the advanced working pattern may be a complicated mowing pattern based on the layout of a garden including bushes, garden islands and other structures.
The advanced operating patterns are generally general in their plan and does not necessarily take all aspects of a garden into consideration, such as elevation changes. Steep slopes may make it difficult for a robotic work tool to perform a specified operating pattern as the robotic work tool may not be able to negotiate the slope or start sliding.
To successfully navigate such complicated operating patterns some contemporary robotic work tools employ satellite navigation, however, these do not work in all areas of a work area if some areas are blacked out from satellite reception.
It is furthermore difficult to specify a correct map for use with a GPS system as a user would have to input all altitudes manually. Even if the GPS were to be used for generating the map, the low accuracy of the GPS would inevitably lead to an incorrect map.
There is thus a need for a manner of enabling reliable operation of a robotic work tool even in situations where the robotic work tool may not be able to receive reliable and accurate signals.